The present invention relates to an improved distal femoral resector guide. Applicant herein is the patentee of prior U.S. Pat. Nos. 4,773,407 and 4,907,578. These patents teach method and instruments for resection of the distal femur. These instruments have proven effective in orthopedic surgery. However, in order to utilize the instruments in Applicant's prior patents, it was necessary to form a flat plane on the superior femoral cortex to receive the base of the instrument. In this regard, reference is made to FIG. 1 herein which corresponds to FIG. 5 in each of Applicant's prior above-mentioned patents. FIG. 1 herein shows the distal end of the femur 10 with the reference numeral 11 referring to the flat plane which has been formed on the anterior femoral cortex through filing or other means. Reference numeral 15 shows the portion of the distal femur which is to be resected using the instrument disclosed therein as well as herein with the reference numeral 13 depicting the distal surface of the femur which is created when the portion 15 thereof is resected.
With reference, now, to FIG. 2, a normal, healthy, unresected distal femur is designated by the reference numeral 20 and is seen, in particular, to include condyles 21 and 23 which form a notch 25 therebetween at the anterior femoral cortex thereof.
With reference to FIG. 3, a corresponding view of the distal femur 20' is shown with the distal femur 20' also including condyles 21' and 23'. In FIG. 3, note the build-up of osteophytic bone on both anterior femoral condyles. The distal femur 20' exhibits osteophytic build-up generally designated by the reference numeral 27 which is evidence of advanced arthritis of the bone at that region. As is clear from comparing FIGS. 2 and 3, the osteophytic build-up obscures the notch which normally exists at the anterior femoral cortex. Such build-up renders the installation of a total knee prosthesis more difficult. As such, a need has developed for a distal femoral resector guide which can accommodate to the osteophytic build-up of arthritic bone on the distal femur, which device may be employed with reduced invasiveness as compared to the prior art.
As is known, in resecting the distal femoral condyles, the resection plane must be perpendicular to the mechanical axis of the femur in the transverse plane while also being perpendicular to the anterior femoral cortex in the sagittal plane. As is known, aligning a resection in these two planes is difficult. In the current state of the art, two methods have been employed to attempt to precisely determine the appropriate alignment of the distal femoral resection with respect to the transverse and sagittal planes. These methods employ either extramedullary alignment means or intramedullary alignment means. Each of these methods inherently includes its own inaccuracies.
In the case of the extramedullary means, the center of the femoral head has to be radiologically determined and marked externally on the patient. The use of trial and error to find the center of the femoral head and accurately locate the external marker on the patient is time consuming. Also, improper positioning of the x-ray machine directly over the center of the femoral head introduces the error factor known as "parallax". Also, alignment rods presently used have to be extended away from the center of the rotation of the bone and, consequently, there can be a significant error with any rotation of the distal femur from neutral. For these reasons, extramedullary alignment of the distal femoral cut fell out of favor in the late 1980s and the intramedullary rod has become popular.
With the intramedullary rod, a rod is placed through a drill hole in the intracondylar notch into the femoral canal and a predetermined difference between the anatomical axis of the femur and the mechanical axis, the so-called tibial femoral angle, is dialed in by a mechanical means and the perpendicular cut is then made through the transverse axis. Unfortunately, there are a number of inherent errors of the intramedullary alignment means. Not uncommonly, the intramedullary canal is quite large and the rod can be misaligned up against one cortex or the other. An error in a large intramedullary canal can be up to 2-3 degrees. Because the intramedullary rod is hidden from the surgeon's view, he has no way of determining this inherent error. Also, the intramedullary canal on the sagittal plane is curvalinear, and can cause mispositioning of the rod depending upon the entrance hole, either in the anterior or posterior direction, affording the rod an inaccurate means of determining a perpendicular cut to the femur in the sagittal plane.
Applicant has discovered that the only reliable way to make a perpendicular cut to the anterior femoral cortex in the sagittal plane is to locate the distal femoral cutter off the anterior femoral cortex. This task is particularly difficult to do unless the anterior femoral cortex cut is made first and indexed from the anterior femoral cortex. This requires a separate cutter which most systems incorporate. However, if there were a means to key the sagittal plane of the distal femoral resector off the anterior femoral cortex without the need to resect the anterior femoral cortex, this task could be accomplished by a single instrument.
However, there are two major problems to overcome. The first is the fact that, as explained above, on some knees there is a large osteophytic build-up of bone over the anterior femoral condyles. The anterior femoral cortex can be almost 1/2 inch lower than the anterior femoral condyles. Secondly, this build-up of osteophytic bone varies in distance from the intercondylar notch to the anterior femoral cortex depending on the size of the patient. Therefore, there must be an ability of the instrument to extend beyond the osteophytic build-up and to get down to the plane of the anterior femoral cortex.
It is with these problems in mind that the present invention was developed.